- Posted in: Blog
- By Ann Marie
Think about the last time you held a medical device. Did you notice the comfortable grip, the sleek build, the ease of control? There is a very good chance that silicone overmolding may have played a key role in that experience. This specialized manufacturing approach seamlessly bonds silicone to other materials, creating durable, ergonomic, and user-friendly devices. From surgical instruments to pacemaker connectors, overmolding enhances functionality, safety, and performance. But beyond aesthetics and comfort, there’s a complex material science at work — one that defines modern medical device innovation.
Introduction to silicone overmolding in medical manufacturing
Silicone overmolding has become an essential process in modern medical manufacturing, enabling engineers to combine the strength of rigid substrates with the flexibility and biocompatibility of silicone. By molding Liquid Silicone Rubber (LSR) directly onto components, manufacturers can create seamless, multi-material assemblies that enhance both function and user comfort.
This technique eliminates secondary bonding steps, improves part reliability, and allows for ergonomic designs that meet strict medical and regulatory standards. It’s used across a wide range of devices — from handheld instruments and catheters to implantable components — wherever comfort, durability, and patient safety are critical.
As a pioneer in silicone processing and complex medical molding, ProMed applies over three decades of expertise to refine this process for scalability, consistency, and compliance. Our company’s work demonstrates how overmolding bridges innovation with real-world manufacturing performance.
The science behind silicone overmolding
At its core, this process is driven by material chemistry, surface modification when appropriate, and precise process control. It involves molding a layer of silicone directly onto a substrate, forming a durable chemical or mechanical bond. Depending on the material combination, bonding may be enhanced through surface treatments such as plasma activation or chemical priming.
Silicone’s unique properties — including biocompatibility, thermal stability, chemical resistance, hypoallergenic behavior, and dimensional stability — make it a preferred choice for medical applications. LSR offers flexible durometer ranges (LSR: 10–80, HCR: 20–80), allowing engineers to fine-tune mechanical properties for specific performance requirements.
Types of overmolding processes
Silicone overmolding encompasses several advanced techniques that allow manufacturers to combine multiple materials into a single, unified component. Two of the most common methods used in medical device production are insert molding and multi-shot molding.
Both approaches enable the creation of precise, multi-material designs that enhance performance, comfort, and reliability in medical devices. Understanding how each process works (and where they excel) helps guide better development and manufacturing decisions.
Insert molding and multi-shot technologies
Insert molding and multi-shot molding represent the foundation of high-performance overmolding.
Insert molding involves embedding a pre-fabricated substrate — such as a metal or thermoplastic component — into a mold before injecting silicone around it. This creates a strong, integrated bond without the need for adhesives or secondary assembly.
In contrast, multi-shot molding involves the injection of multiple materials sequentially within the same machine. This method delivers seamless transitions between materials, eliminates handling steps, and is particularly effective for high-volume production runs.
ProMed’s expertise spans both techniques, offering precision control for small-scale prototypes as well as fully automated, multi-material production systems.
Insert molding for medical components
When a medical device requires the strength of a rigid substrate combined with the flexibility and biocompatibility of silicone, insert molding is ideal. The process involves placing metal or plastic inserts into the mold before the injection of LSR, forming a durable mechanical or chemical bond.
This approach supports a wide range of device types, from micro-molded sensors to large, ergonomic handles, and allows for manual or robotic placement depending on production scale. ProMed applies this method to achieve reliable adhesion, tight tolerances, and long-term performance for critical medical applications.
Multi-shot molding and alternative processes
Multi-shot molding takes integration a step further through the injection of two or more materials within a single molding cycle. This enables precise material distribution, superior bonding, and consistent repeatability across large volumes.
Because no handling or repositioning is required, multi-shot molding reduces cycle time while improving dimensional accuracy and cleanliness, which are key benefits for regulated medical environments. Compared with traditional injection molding, overmolding allows multi-material bonding without adhesives.
In addition to multi-shot molding, ProMed also utilizes transfer and compression molding techniques when they better suit a project’s design, volume, or material requirements. This versatility allows the company to tailor every molding process to the device’s intended use, ensuring optimal performance and efficiency.
Material selection for overmolding applications
Material selection is a critical first step in designing overmolded medical devices. Overmolding inserts can include medical-grade thermoplastics such as polycarbonate, ABS, and PEEK, or metals like stainless steel and aluminum, each offering properties like impact resistance, transparency, or lightweight strength. These plastic substrates provide designers flexibility in balancing durability, weight, and chemical resistance.
Equally important is bonding compatibility with silicone elastomers. LSR enables precise shot control and faster cycle times, while HCR supports larger parts and broader formulation options, ensuring durable adhesion and functional performance. Understanding the complete molding process is critical to achieving precise adhesion and dimensional accuracy.
When evaluating materials, think about factors like:
- Mechanical and chemical compatibility with the overmolded silicone. This ensures the materials remain stable over time and resist reactions or degradation.
- Sterilization method compatibility. Verify that the material maintains integrity through gamma, EtO, or autoclave cycles without affecting performance.
- Desired durometer or flexibility. Choose the right balance between user comfort and device functionality for consistent use.
- Thermal resistance and dimensional stability. Confirm that parts maintain their shape, tolerances, and mechanical properties during molding and in service.
- Surface finish and texture. Structure surfaces to maximize bonding strength and minimize the risk of delamination, ensuring long-term durability.
Careful consideration of these factors ensures reliable performance and regulatory compliance across every overmolded medical device.
Design considerations for successful overmolding
Geometric features and tooling requirements play a decisive role in the success of overmolding in medical device creation. Proper optimization enhances bond strength, reduces defects, and ensures parts meet tight specifications while remaining cost-effective at scale.
Geometric features and tooling requirements
Careful attention to geometric design and tooling is essential. Mechanical interlock features help achieve reliable bonding and maintain device performance, while mold layout and in-house tooling capabilities influence manufacturability and overall quality.
Mechanical interlock features for optimal bonding
To ensure effective bonding, consider mechanical interlocks such as:
- Undercuts and through-holes, which provide positive locking and reinforce silicone adhesion to the substrate
- Circumferential grooves, designed to enhance sealing performance and prevent fluid or gas leakage
- Surface textures, which are engineered to increase the bonding surface area and improve mechanical grip between materials. This includes practices like plasma etching of the surface or utilizing a primer layer.
When combined with expert silicone molding practices, these features ensure precise material interfaces, prevent delamination, and produce fully bonded, durable components suitable for medical device applications.
Mold design and in-house tooling capabilities
Mold design requires thoughtful gate placement, venting strategies, and temperature control zones. Preheating substrates and maintaining LSR cavity temperature are crucial for uniform adhesion.
In-house tooling capabilities allow faster iterations, reduce reliance on external vendors, and maintain consistent quality across all production runs.
Sterilization and post-molding processing
Ensuring sterility is critical for overmolded medical devices. Sterilization methods must preserve silicone-substrate bond integrity and material properties.
Common approaches include:
- Gamma radiation, effective for microbial inactivation, but may alter plastic coloration and requires verification of material stability and bond strength
- Ethylene oxide (EtO), which is compatible with most materials but requires careful degassing post-sterilization to remove residual gas and ensure device safety
- Autoclave sterilization, suitable for high-temperature plastics and silicone, though repeated cycles may impact component dimensions and require dimensional verification
Post-molding operations, such as deflashing, precision trimming, and ultrasonic cleaning, performed in Class 7/8 cleanrooms or other controlled environments minimize foreign material contamination and prepare components for final assembly. Careful sterilization and post-processing ensure reliability, compliance, and long-term performance in modern medical device applications.
Troubleshooting common overmolding defects
Even with precise overmolding, defects can arise in medical device components. Common issues include delamination, poor adhesion, and interfacial separation, often caused by inadequate surface preparation, insufficient cure time, or incompatible material combinations.
Preventative measures include validated cleaning protocols, proper substrate preheating, and confirmed cure profiles. In some cases, adhesion promoters or surface treatments may be required. Robust quality management systems, like those at ProMed, ensure these defects are identified and corrected quickly, maintaining compliance and part integrity.
Critical applications in medical device manufacturing
Silicone overmolding plays a pivotal role across numerous medical device applications, enhancing functionality, safety, and user experience. Some key applications are:
- Soft-grip handles on surgical instruments that improve tactile control and reduce hand fatigue during procedures
- Drug delivery components, providing chemical compatibility and leak-free performance
- Wearable medical devices that offer comfort, durability, and improved user interaction
- Seals and gaskets in diagnostic equipment to help maintain integrity under repeated sterilization cycles
- Seals in endoscopic or robotic systems to prevent fluid ingress.
- Custom connectors or buttons in electronic or monitoring devices, combining ergonomic design with precise functionality
- Overmolding sensors, whether diagnostic or used in robotic applications to improve feedback and control
These examples illustrate how overmolding enables superior performance, reliable bonding, and a user-focused approach in modern medical devices.
Quality control and regulatory compliance
High-quality overmolded components require strict adherence to quality systems, testing protocols, and regulatory standards. ISO 13485:2016 certification and FDA registration provide the framework for compliant production.
Design controls, process validation, and risk management must be rigorously applied. Continuous monitoring, traceability, and documentation, combined with testing for bond strength, biocompatibility, and material properties, safeguard reliability. Dimensional inspections confirm geometric tolerances and stability, while sustainable supply and lifecycle support ensure consistent, compliant production.
Frequently asked questions:
1) What is the difference between silicone overmolding and two-shot molding?
Silicone overmolding places a pre-made substrate — plastic or metal — into a mold before injecting LSR around it. Two-shot molding, by contrast, produces both materials sequentially in the same machine, transferring parts automatically between cavities.
Overmolding allows more substrate flexibility, including pre-treated plastics or machined metals, and lower tooling costs for smaller runs. Two-shot molding provides superior bonding, hot-to-hot material contact, and precise alignment at lower cost.
2) Can silicone overmolding be used for implantable medical devices?
Yes. Medical-grade LSR that meets USP Class VI and ISO 10993 biocompatibility standards is routinely used in short-term and long-term implantable devices.
ProMed offers expertise in material selection compatible with body tissues, sterilization validation to maintain bond integrity through multiple cycles, and full regulatory support for FDA 510(k) submissions and PMA applications. Collaborative development ensures timelines align with clinical trials while maintaining compliance and patient safety.
3) What are the typical lead times for overmolded medical device components?
Lead times depend on part complexity, tooling, and production volume. Prototype tooling and initial samples from ProMed’s Development Center typically take 5 to 6 weeks, while in-house production tooling may require 10 to 14 weeks.
ProMed’s complete in-house engineering and fabrication capabilities streamline timelines by eliminating external vendor coordination. Once validated, production runs can be scheduled across four facilities totaling over 134,000 sq ft of cleanroom and manufacturing space, supporting both low- and high-volume needs.
4) How do you ensure consistent bonding between silicone and substrate materials?
Consistent bonding relies on controlled parameters such as substrate preheating (160 to 250°F), mold cavity temperatures (300 to 390°F for LSR), and validated cure times.
ProMed uses qualified LSR formulations with documented adhesion, destructive bond strength testing, and IQ/OQ/PQ process validation protocols. Statistical process control monitors key parameters in real time, while mechanical interlocks like undercuts and through-holes reinforce chemical bonding.
All procedures are documented under ProMed’s ISO 13485 quality management system, ensuring repeatable results across production batches.
5) What sterilization methods are compatible with silicone overmolded parts?
Medical-grade LSR overmolded components withstand gamma radiation (25 to 50 kGy), ethylene oxide (EtO), autoclave (250 to 275°F), and e-beam sterilization.
Compatibility depends on substrate material; some thermoplastics may degrade under gamma or high-heat steam. ProMed conducts sterilization testing and validation to confirm that both materials and bond integrity remain stable, including bond strength checks, dimensional verification, and material property confirmation to meet device specifications and expected shelf life.
6) What industries besides medical devices use silicone overmolding?
ProMed applies overmolding across security and defense applications (environmental seals, access controls, ITAR-compliant equipment), consumer products (kitchen tools, personal care items, electronic grips), automotive (seals, connectors with heat resistance), and industrial applications (high-temperature gaskets, protective grips).
Expertise in highly regulated sectors ensures adherence to stringent quality standards, delivering durable, reliable components for any demanding environment.
7) Why is surface preparation important in overmolding?
Proper surface preparation ensures strong adhesion between silicone and substrate. Cleaning, degreasing, and optional plasma or corona treatments reduce contaminants and enhance chemical or mechanical bonding.
ProMed validates surface prep protocols for each material combination to prevent delamination, voids, or weak bond lines, ensuring device reliability and regulatory compliance across production batches.
8) Can silicone overmolding accommodate micro-scale medical components?
Yes. ProMed’s advanced molding capabilities include micromolding and precise multi-cavity tooling to produce components at sub-millimeter scales.
This enables the integration of complex features such as micro-channels, seals, and soft-touch interfaces while maintaining dimensional stability and biocompatibility for medical applications.
9) What role does mechanical interlocking play in overmolded designs?
Mechanical interlocks such as undercuts, through-holes, and surface texturing increase bonding surface area and reinforce adhesion beyond chemical bonds.
Incorporating these features reduces delamination risk and enhances durability, especially for devices that undergo repeated sterilization or mechanical stress. ProMed integrates these considerations into tooling design for reliable, repeatable outcomes.
10) How do you maintain quality control across high-volume overmolding runs?
Consistent quality requires real-time monitoring, statistical process control, and process capability studies (Cpk) to track dimensional and mechanical tolerances.
Under its ISO 13485 quality management system, ProMed combines automated inspection, destructive bond strength testing, and continuous audits. This ensures that each component meets regulatory standards and maintains performance across every production cycle.
Conclusion
Silicone overmolding is a cornerstone of modern medical device development, combining precise materials, advanced processes, and thoughtful engineering to create functional, durable, and patient-friendly components. Understanding geometric considerations, sterilization requirements, post-molding processing, and quality control ensures devices meet the highest regulatory and performance standards.
By mastering these techniques and integrating robust monitoring and troubleshooting practices, manufacturers can deliver reliable, innovative, and safe medical devices that improve usability and patient outcomes across the healthcare industry.
For teams looking to bring high-quality, overmolded devices to market, ProMed offers deep expertise, full regulatory support, and in-house capabilities from prototyping through production. Contact ProMed to explore how our solutions can help streamline development and ensure consistent, compliant results.
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